Assuring the safety of fluid milk, related dairy products and juices while maintaining quality and increasing the shelf life of products is a significant challenge for the food industry. Thermal inactivation of spoilage and pathogenic microorganisms (i.e. Thermal pasteurization) is the most widely used method to achieve these goals. For nearly 100 years milk and other foods have been thermally pasteurized to inactivate microorganisms which might cause human disease (i.e., to make milk safer) and to inactivate inherent enzymes and spoilage microorganisms (i.e., to make milk last longer).
Unfortunately, thermal pasteurization can have detrimental effects on flavor and nutritional quality. Although thermal pasteurization improves safety and prolongs shelf life, it often causes a decrease in flavor quality (cooked flavor), nutritional content (vitamin loss), and other quality factors (brown color). Additionally, recent research suggests that a heat resistant strain of the milk-borne pathogen Mycobacterium paratuberculosis may survive current pasteurization conditions (Grant et al., 1998).
Many attempts to mitigate the undesirable effects while maintaining the desirable effects of thermal pasteurization have been undertaken. Nearly all of this work has focused on improved methods of transferring heat into and out of the product to minimize thermal damage. For example, dozens of improved heat exchangers have been designed including processes known as HTST (high temperature short time) pasteurization and, more recently, UHT (ultra high temperature) processing.
An alternative approach would be to re-formulate the product (e.g., milk) to enhance the effect of heat on microbial death. For example, lowering the pH by adding an acid increases the rate of microbial inactivation. It is well known that reducing pH causes an increase in the thermal death of microorganisms but the addition of mineral or organic acids for this purpose is not acceptable under current regulations (Pasteurized Milk Ordinance, 1995). Thus, although this approach has been amply demonstrated, it has not been practiced because whatever is currently known to be effective when added to the milk would remain in the milk and ultimately be consumed. Regulations around the world prohibit such additives, especially in the case of milk.
Shelf life is also a major issue facing the industry. Many companies that choose to increase the heat treatment of their product to produce a product having a lengthened shelf life do so at a considerable expense and a loss of flavor quality.
What is needed is a process that assures food safety, maintains quality, and improves shelf life with minimal product damage.